The Kazal inhibitors are serpins with sequence similarity to the bovine pancreatic secretory trypsin inhibitor (PSTI) which appear to be present in all vertebrates. Some examples of Kazal-type inhibitors include the acrosin-trypsin inhibitor (ATI), and PEC-60 (peptide with N-terminal Glu and C-terminal Cys) isolated from porcine intestine.
The precursor of PEC-60 is 86 amino acids long and has a 26 amino acid signal sequence. PEC-60 is a secreted protein with about 41% similarity to PSTI, but it does not inhibit trypsin nor does not affect basal plasma insulin levels. The known roles of PEC-60 are the in vivo inhibition of glucose-induced secretion of insulin and the regulation of cyclic adenosine monophosphate (cAMP) levels through dose-dependent reduction of cAMP formation. High levels of PEC-60 have been recorded in bone marrow and peripheral blood and moderate levels, in spleen. The results of radioimmunoassays show that pig PEC-60 is formed, stored and secreted from monocytes. High levels of PEC-60 are known to be immunoreactive in catecholamine neurons (Laazik, J. and R. Sillard (1993) Biochem. Biophys. Res. Commun. 197:849-52; Metsis, M. et al. (1992) J. Biol. Chem. 267:19829-32; and Ahren, B. et al. (1992) Pancreas 7:443-6).
Analysis of the amino acid sequences of Kazal-type inhibitors shows some regions of similarity with other serpins, but the highly conserved cysteine residues at positions 36, 46, 54, 65, 68 and 86 solidify their group association and provide some alignment with the beta subunits of the glycoprotein hormones, chorionic gonadotropin, luteinizing hormone, follicle stimulating hormone and thyroid stimulating hormone. The reported active site, P1-P', for the Kazal type inhibitors, resides in the residues at positions 47 and 48 and may be responsible for the specificity of the inhibitor (Liepinsh, E. et al. (1994) J. Mol. Biol. 239:137-53); Fink, E et al. (1990) FEBS Lett. 270:222-4).
PEC-60 has been shown to reduce dopamine utilization in the caudate nucleus which suggests that PEC-60 has a role in activities or diseases of the central nervous system (Laasik, supra). A Kazal-type inhibitor with amino acid sequence similarity to PEC-60 was recently identified in rat bile/pancreatic juice and has been shown to stimulate the release of cholecystokinin (Agerberth, B. et al. (1989) Proc. Nat. Acad. Sci. 86:8590-4) ATI, which is synthesized in the testes and has been isolated from seminal fluid of several species, may play a role in regulating the effects of glycoprotein hormones. Given the region of sequence similarity between the Kazal-type inhibitors and the beta subunits, inhibition may depend on blocking the glycoprotein hormone receptors in the reproductive tissues (Perry, A. C. et al. (1993) Biochim. Biophys. Acta 1172:159-60; Fink, supra). PSTI is expressed in internal organs such as liver and pancreas, in response to inflammatory cytokines. Expression was most pronounced in tissues from patients with liver, pancreatic, gastric or colonic cancers, but it has also been associated with Crohn's disease, chronic hepatitis and cirrhosis (Ohmachi, Y. et al. (1994) J. Hepatol. 21:1012-6, Int. J. Pancreatol. 15:65-73, and (1994) Int. J. Cancer 57:139; Halme, L. et al. (1993) Scand. J. Clin. Lab. Invest. 53:359-66). Similarly, tumor-associated trypsin inhibitor is detected in the serum and urine of patients with ovarian or cervical cancer. In ovarian cancer, the level of inhibitor detected serves as a marker for the grade or stage of the tumor (Medl, M. (1995) Br. J. Cancer 71:1051-4; Pectasides, D. (1994) Am. J. Clin. Oncol. 17:307-12).
The discovery of polynucleotides encoding Kazal-type inhibitors, and the molecules themselves, presents the opportunity to investigate the progression of various cancers and tumors. Discovery of molecules related to PEC-60 and related Kazal-type inhibitors satisfies a need in the art by providing new diagnostic or therapeutic compositions useful in the diagnosis and treatment of such cancers and tumors.